".....just 200 square miles of the Sahara desert could create enough solar energy to supply all the power the whole world needs, he says."

Quick cross check for credibility:

World average power consumption in 2008 was estimated at 1.504 x 10^13 W in 2008 (source Wikipedia, so subject to error, perhaps)

200 square miles is around 5.18 x 10^8 m²

Current PV panel efficiency is around 18%

Average daily irradiance in the Sahara may be around 1000W/m²

Average period of irradiance may be around 12 hours per day

Assume that panels cover the whole 200 miles²

Panel power output during the 12 hour irradiance period may be around 9.33 x 10^10 W

Average daily power output may be around half of this, so around 4.66 x 10^10 W

So, it looks like an incredible claim, as the power produced by 200 miles² of the Sahara covered with 18% efficient PV panels will only be around 0.3% of the 2008 world average power usage. Even if there are some errors in the above assumptions I doubt they are big enough to still seriously question the credibility of this Dr Sterner. If he's wildly exaggerated on this point, how much of the remainder of his claims can be trusted?

I'm afraid I'm naturally a bit cynical about claims for new technologies, although I do agree in principle that this particular one is interesting. It's just a pity that the originators seem to feel the need to tell porkies.......

Hmm. Did wonder if that was a slip of his tongue, but considered he wouldn't be daft enough to make the prediciton if he didn't know something we didn't. Everything I've read has always talked about the Sahara having the potential to power EUROPE.

Perhaps if someone cared to do the math on how much methane the pv/wind generated electricity would produce and stack it up against predicted world TRANSPORT useage a decade ahead?

Not knowing the context of the 200 miles2 quote is always difficult although further investigation of Dr Michael Sterner brought up this quite interesting report which certainly puts a spanner in the works of our Professor McKay as it actually looks like a credible action plan for a renewable future.

http://www.eubia.org/uploads/media/1._Fraunhofer-IWES_M.Sterner.pdf

Lat 22.5 and Long 0 (about where the Sahara is) has 6.1 kWh.m^-2

18% of that that is 1.1 kWh

200Miles ^2= 517999700

517999700*1.1=569799670 kWh

Or 569.8 GWh (around 2.05128 TJ)

So how much is needed, I think world energy use is somewhere close to 2.95 EWh or1.06*10^19J (not sure what to the power 18 is called)

"For those who persist in arguing that we can grow enough fuel for future energy needs it shows just why concentrating on utilising solar and wind makes more sense."

Hmmm. Absolutely no chance for nuclear then! Ho hum. Round four. Or is it five now?

<blockquote><cite>Posted By: Joiner</cite>Hmmm. Absolutely no chance for nuclear then! Ho hum. Round four. Or is it five now?<img title="" alt="" src="/forum114/extensions/Vanillacons/smilies/standard/confused.gif"></img></blockquote>

As someone who started their career in the nuclear industry (for the old UKAEA back in the very early 1970's) I have always thought that nuclear power has been grossly and unfairly maligned by the press over the years. All power generation creates pollution and safety problems, even seemingly clean technologies like wind and solar.

The worst, by far, in terms of global pollution and absolutely colossal loss of life is coal, probably followed by gas and oil, with nuclear a long way behind. Although nuclear creates severe pollution problems at both ends (mining ore and disposing of the tiny amount of highly toxic and dangerous waste it creates) in the overall scheme of things it's far "cleaner" and safer than other readily available fuels (other than solar/wind etc).

Turning wind or solar energy into extremely useful hydrocarbon molecules such as Methane or Methanol sounds like a great idea but the process would have heavy conversion loses and at the low capacity factors that such renewables operate would be grossly uneconomic. Even a baseload electric plant with 90%+ capacity factor electrolysing H2 and CO2 would not be considered viable at any time in the near future.

I dont think 200 sq miles is very far out based on this report which assumes 8% conversion rate. If you substitute the more realistic 20% conversion rate obtainable from thermal solar than Dr Sterner figures are very similar obviously converting from km to miles.

http://www.ez2c.de/ml/solar_land_area/

Steamy- This link from site you detail is interesting.
http://www.rspb.org.uk/news/288724-study-exposes-green-failings-of-wood-fuel-power-plans-
Above article understates import requirement at 68%, Gov DECC/Arup June report details 90% import. Already creating concern re forest impact in US.

I suspect my calculations are awry. There is also a difference between primary energy and delivered energy. If PV is used then what is produced at the panel is only slightly higher than what is delivered, if biomass is used to generate electricity, with our current technology, then there is a large difference between primary and delivered. If I get time over the weekend I shall do a bit more research and check my numbers, rather than spend 5 minutes at lunchtime, while having a conversation and listening to the news because I think my figure of 6.1 kWh is a daily figure.
So:
6.1 kWhd^-1m^-2 * 0.18 overall efficiency * 517997622 m^2 = 568761389 kWhd^1 or 569 GWhd^-1. This translates to 2.05 PJ.

World mean usage is 48 kWhd^-1person^-1. Population is around 7 billion
so:
48 kWhd^-1person^-1 * 7 billion* 365 days = 122.64 PWhy^-1 or 441.5 PJ

Just can't leave it alone. These numbers are so large they do not make sense to me.

Yes, CCGT reach about 61% efficiency based on the lower heating value for the fuel but making gas from first principals involves significant penalties. Such C02 and H20 chemical reductions plants performing a "syntrolysis" process would much prefer a nice steady baseload electricity supply from a dependable non fossil source rather than being based on weather dependant supplys - tho I do believe that renewable energy stored chemically as methane/anhydrous ammonia is the only practical way to make wind/sun power reliable enough to be something more than the marginal power source it is today.

JSH, not sure if the majority of industrial use is heat, I would have thought that rotating machinery may well be higher. Commercial stuff may be different, though I suspect that a lot is for lighting and IT (which generates a lot of heat). Health almost certainly uses a lot of heat.

Actually I gave up speculating and had a look at DUKES

I agree what we can vastly reduce our electrical consumption, currently working on my domestic data at the moment (waiting for Excel to recalculate). Part P may well have to be used to cover internal lighting/small loads, as there are safety issues from fire as well as shock. MCS/FITs has seriously skewed the whole domestic energy market. If we had asked people 10 years ago if they would have been happy exporting at the same price as importing they would have said yes, but then people forget that retail and wholesale prices are different.
Trouble is really storage (yet again), whereas the grid does not store anything, it does distribute to where it is needed in a very effective way with lower losses than local battery storage, heat cannot easily be transported and would require a very expensive new infrastructure, but it can be stored locally quite effectively. So yes, a better mix of heat storage and electrical distribution may well reap dividend, with the caveat that reduction happens first.

JSH

What your asking for already exists

http://www.coolenergyinc.com/solar.html

The principal works even better using thermal oil as it allows direct cooking using a thermal oil oven and the production of steam on demand.

The energy reduction thing is getting there, at least for big items like freezers, washing machines etc, but what really surprised me a few years ago (around the time I started getting a bit anal about measuring household electrical power consumption) was just how much power was being consumed (mainly by producing waste heat) by low voltage appliances.

Like many households, ours was awash with little power adapters, running everything from the cordless 'phone through to laptops, a wireless modem, external PC network drive, scanner, mobile 'phone chargers, electric toothbrushes, you name it. I counted over a dozen of the things in our house, many of which seemed to be on more often than off. Overall these pesky little blighters were using around 55W, 24 hours a day, with the vast majority of that being waste heat, at an annual cost today of over £50. A look at them revealed that many of them produce most waste in the 240V to low voltage DC conversion. I was also surprised to see how high the standby power consumption was on things like PCs and printers. My fix has been to only power these things when they are needed, with time switches to turn off things during times they aren't needed (like the cordless 'phone at night, and relying on the ordinary 'phone only for that period).


renewablejohn,

I know that the technology already exists, which is why I mentioned it. The problem is primarily one of high capital cost, plus a natural conservatism towards change of this type (when looking at a new build I was amazed at how reluctant a lot of trades were when it came to using different or unfamiliar technology in a house).

How many people realise, for example, that it's perfectly feasible to build a solar (or any other heat source) powered fridge, with no moving parts? Anyone who can recall the time when gas flame powered absorption refrigerators were commonplace (as they still are in caravans, I believe) will understand that a solar powered heat pump can work adequately well to cool a well-insulated chamber. Add a large thermal mass to maintain the low temperature at night and you could have a viable alternative to a fairly power-hungry electrical device. Why not build such a system in to new houses, as a small cold room or larder, for example?

Joiner,

I agree, electricity is just too useful to suggest doing away with it. My point is primarily that we should use it sparingly and only when we have no reasonably practical alternative. I suggest not using it for high power heating, where the overall system efficiency (heat source - heat engine - generator - distribution network - point of use) is going to be quite poor (certainly sub 60% overall, I believe). For example, one slightly odd move in recent years has been the change from hot and cold fill domestic appliances, to ones that are cold fill only. The manufacturers claim this is because of the need for cooler water than that provided by a hot water system. One side effect is that these things now all use big electric heaters to heat the water they use. Wouldn't it be better if these things could use low grade solar heated water, instead, or even mix more efficiently heated DHW with cold to get the right temperature?